>>1110104I just searched "cyclocross frame" on the bay and the first page of results shows a bunch of options under $275 with shipping if you don't need anything unusually large or small. If you need to go cheaper than that, you should be looking locally (shops, swap meets, craigslist). Paying retail prices anywhere will cost you a bunch.
If you want to go really, really cheap, almost any bike with canti studs can be turned into a fun cyclocross machine - you could get riding sooner by putting your parts on a mediocre frame for now then upgrade the frame later. I used a Shogun touring frame as the base for a CX/gravel bike for a couple years and had lots of great rides on it before I upgraded to something lighter with a shorter wheelbase.
